A high-speed train car or locomotive may be supported on two trucks or bogies, each truck or bogie having two or more powered and/or non-powered axles carrying wheels. Each powered axle is driven by a motor through a gear train that includes a pinion gear driven by the traction motor shaft and driving a bull gear mounted on the axle. By way of example, a truck or bogie for use on a diesel-electric rail vehicle includes a frame, an axle mounted on the frame by journal bearings, wheels on the axle, a bull gear on the axle, and a motor and pinion gear attached to the frame. The pinion gear is operably coupled to the bull gear for the traction motor to move the pinion and thereby the bull gear, axle, and wheels. Such a system can result in disadvantageously high forces on the underlying track, due to inertia of “unsprung” mass.
To explain further, mass supported directly on an axle (i.e., not through a vehicle's primary suspension) is known as “unsprung” mass. In operation of high-speed rail systems, the presence of unsprung mass can induce low frequency dynamic forces at the interface of each wheel with the rail. These low-frequency dynamic forces at the wheel-rail interfaces can cause degradation of track geometry.
It is known that track maintenance is the largest expense for operation of a rail corridor. Thus, it is desirable to reduce the unsprung mass of each truck or bogie on a high-speed rail car or locomotive, so as to mitigate the expense of track maintenance.
Unsprung mass may be reduced by supporting the traction motor and/or the gear train of each axle from the truck frame, rather than directly from the axle. For example, leaf springs may be used to support the traction motor with swaying or surging motions relative to the truck frame. However, supporting a motor and/or gearbox from the truck frame (a “suspended motor” configuration) can have the undesirable effect, during operation of the high-speed rail system, of producing relatively large displacements between the traction motor shaft and the axle as compared to conventional trucks or bogies having axle-mounted motors and gearboxes. These large displacements detract from dynamic stability and track-following of the rail vehicle, thereby limiting the achievable speed. The large displacements also increase mechanical stress and wear on power train components, in turn reducing the mean-time-between-failures (MTBF) and maintenance life span for suspended motor configurations, relative to conventional truck frame configurations.
In view of the above, a need exists for relatively simple apparatus that will effectively reduce unsprung mass on a high-speed rail truck, while also mitigating displacements between a motor shaft and a power axle driven from the traction motor shaft.